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oxmox11
User level: Level 1 (53 points)

Mac Studio: File transfers fail with Thunderbolt Bridge and other networks

Apple Feedback Assistant ID: MISSING


DESCRIBE THE BUG:


File transfers and remote Final Cut Pro library access fail when Thunderbolt Bridge and another network connection are active simultaneously between two Mac Studio computers.


Thunderbolt Bridge works correctly on its own. Without Thunderbolt Bridge, remote libraries also open correctly over Wi-Fi, Ethernet, or both together. The problem occurs specifically when Thunderbolt Bridge is active alongside Ethernet, Wi-Fi, or both.


In the affected configurations:


- The remote Mac and its shared volumes appear in Finder’s sidebar as expected.

- The shared volumes can be mounted and browsed.

- File copying starts but stops partway through, without displaying an error number.

- Remote Final Cut Pro libraries do not finish opening.

- After an unsuccessful library-opening attempt, Final Cut Pro on the host Mac reports that the library is in use by the client Mac.

- Interrupted copies have left greyed-out, incomplete destination folders that I could not delete through Finder at the time.


This is not isolated to Final Cut Pro. General file copying between the two Macs is also affected.


TO REPRODUCE:


1. Connect the two Mac Studio computers using a Thunderbolt cable and establish a Thunderbolt Bridge connection.

2. Disable Ethernet and Wi-Fi on both computers, leaving Thunderbolt Bridge as the only active network connection.

3. Select the automatically discovered remote Mac in Finder’s sidebar and mount its shared volume.

4. Copy files and open a remotely stored Final Cut Pro library. Both operations work.

5. Quit Final Cut Pro before testing the next configuration.

6. Enable Ethernet while leaving Wi-Fi disabled and Thunderbolt Bridge active.

7. Attempt to copy files or open the remote library. Copying starts but stops partway through, and the library does not finish opening.

8. Repeat with Thunderbolt Bridge plus Wi-Fi only, then with Thunderbolt Bridge plus both Ethernet and Wi-Fi. The same failures occur in each configuration.

9. As a separate control test, shut down and restart without the Thunderbolt connection. Access the shared library using Wi-Fi only, Ethernet only, or both together. The library opens successfully in all three configurations.


EXPECTED BEHAVIOUR:


File transfers and remote Final Cut Pro library access should continue to work reliably when multiple network connections are active.


Enabling Ethernet or Wi-Fi alongside Thunderbolt Bridge should not cause file transfers to stop or prevent libraries from opening.


SPECS:


Host Mac:

- M1 Ultra Mac Studio.

- 128GB RAM.

- 8TB internal SSD.

- Test library stored on a partition of the internal SSD.


Client Mac:

- M5 Ultra Mac Studio

- 96GB RAM.

- 2TB internal SSD.


Software:

- Tested under macOS 26.7.1 and macOS 27, with the same issue on both.

- Final Cut Pro 12.4.


Connection and access:

- Direct Thunderbolt Bridge connection.

- Multiple Thunderbolt cables tested.

- Shared volume mounted by selecting the automatically discovered remote Mac in Finder’s sidebar, rather than manually entering an IP address.


ADDITIONAL COMMENTS:


I tested this extensively with Apple Support. Multiple Thunderbolt cables produced the same result.


Configurations tested:


- Thunderbolt Bridge only: file transfers and remote Final Cut Pro library access work.

- Wi-Fi only, without Thunderbolt Bridge after restart: remote Final Cut Pro libraries open successfully.

- Ethernet only, without Thunderbolt Bridge after restart: remote Final Cut Pro libraries open successfully.

- Wi-Fi and Ethernet together, without Thunderbolt Bridge after restart: remote Final Cut Pro libraries open successfully.

- Thunderbolt Bridge plus Ethernet, with Wi-Fi disabled: file transfers stop partway through, and remote libraries do not finish opening.

- Thunderbolt Bridge plus Wi-Fi, with Ethernet disconnected: file transfers stop partway through, and remote libraries do not finish opening.

- Thunderbolt Bridge plus Ethernet and Wi-Fi: file transfers stop partway through, and remote libraries do not finish opening.


The original library opens normally on the host M1 Mac Studio.


These tests narrow the issue to configurations where Thunderbolt Bridge is active alongside another network connection. Neither Thunderbolt Bridge alone nor ordinary network access without Thunderbolt Bridge reproduces the library-opening problem.


Because the share is mounted through Finder’s automatically discovered sidebar entry, the actual network interface used by the mounted share when multiple connections are active has not yet been verified. The underlying cause remains undetermined.




Posted on Oct 31, 2026 8:15 PM

2 replies

shachar17
User level: Level 1 (18 points)

Oct 31, 2026 10:49 PM in response to oxmox11

Suggested Solutions

1. Adjust Network Service Order (Priority)

macOS determines which network interface to prioritize based on the order listed in your Network settings. When multiple interfaces are active, macOS might be intermittently switching or attempting to route high-bandwidth AFP/SMB traffic over a slower or conflicting interface (like Wi-Fi or standard Ethernet) rather than sticking strictly to the direct Thunderbolt link.

  • How to fix:
    1. Go to System Settings > Network.
    2. Click the Action menu (...) or click the gear icon/three dots at the bottom of the network services list and choose Set Service Order.
    3. Drag Thunderbolt Bridge to the very top of the list (above Ethernet and Wi-Fi).
    4. Move Wi-Fi to the bottom.
    5. Click Apply.

2. Manually Route Traffic via IP Addresses (Bypass mDNS/Bonjour Discovery)

When you mount a shared volume by clicking the automatically discovered Mac in Finder's sidebar, macOS relies on Bonjour/mDNS to establish the connection, which can sometimes bind to an unintended network interface (such as Wi-Fi or Ethernet) even if Thunderbolt is connected.

  • How to fix:
    1. Assign manual static IP addresses to the Thunderbolt Bridge interfaces on both Macs (e.g., Mac A: 192.168.2.1, Mac B: 192.168.2.2, with subnet mask 255.255.255.0).
    2. Instead of clicking the remote Mac in the Finder sidebar, press Command + K in Finder to open the Connect to Server window.
    3. Enter the explicit Thunderbolt Bridge IP address of the host Mac (e.g., smb://192.168.2.1) and mount the volume directly through that interface. This forces the data stream to use the Thunderbolt link.

3. Disable Unused Network Interfaces During Heavy Transfers

As a practical workaround for heavy workloads like video editing and large library transfers in Final Cut Pro, temporarily turning off Wi-Fi and unplugging Ethernet while using the Thunderbolt Bridge ensures zero route-switching interference.

den.thed
User level: Level 10 (99,154 points)

Oct 31, 2026 9:17 PM in response to oxmox11

1) How is your Network Service Order setup…?

Change the order of the network services your Mac uses - Apple Support

I mentioned this, because it sounds like the services might be conflicting, shifting and/or switching from one service to another.


2) How good is your Thunderbolt and other USB cables…?

Resolve Wi-Fi and Bluetooth issues caused by wireless interference - Apple Support

I mention this, because Wi-Fi can suffer interference from poorly shielded high speed cables.


With that setup, I would remove any unnecessary network services and move the Wi-Fi to the bottom of the service order. Test it with Thunderbolt first, Ethernet second and Wi-Fi last. The thought here is, that way the connection between the Mac’s will lock in on Thunderbolt or Ethernet instead of Wi-Fi.

Originally posted at discussions.apple.com/thread/256386744